A method for synthesizing multi-element doped carbon-based microtubes with adjustable diameter by supramolecular self-decomposing template

Abstract

The application discloses a kind of supermolecule self-decomposition template synthesis multi-element doped diameter adjustable carbon-based micropipe method, belong to carbon micropipe preparation technical field, operation steps are as follows: (1) respectively preparation containing melamine (M) or 2,4,6-triaminopyrimidine (TAP) solution A and containing cyanuric acid (CA) or trithiocyanuric acid (TCA) solution B;(2) A liquid drop is added to B liquid, and the supermolecule precursor of M-CA, M-TCA, TAP-TCA is obtained;(3) 2-methylimidazole and sulfur, boron, phosphorus, fluorine and other element compounds are added in the solution of precursor, and after heating and drying, the precursor composite with different diameters is obtained by drying in oven for 24h;(4) it is obtained by calcining at 500-700 DEG C for 1-2h under argon atmosphere;In the application, the synthesized supermolecule as a template has the advantages of self-decomposition, adjustable diameter, and can be partially converted into carbon-based materials;During preparation, adding appropriate drugs realizes multi-element doping in one step, and the method has the advantages of simplicity, low cost and large-scale preparation.

Description

Technical Field

[0001] This invention belongs to the field of carbon microtube preparation technology, specifically relating to a method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using supramolecular self-decomposing templates. Background Technology

[0002] Since the advent of carbon nanotubes, tubular carbon materials have been developed for over two decades. As a typical one-dimensional carbon nanomaterial, carbon nanotubes, with their unique hollow tubular structure, excellent mechanical properties, high electrical conductivity, and high specific surface area, have shown great application potential in materials science, energy storage, electronic devices, catalysis, separation membranes, and composite materials. Carbon microtubes are also a unique carbon material, with physicochemical properties very similar to carbon nanotubes, differing only significantly in diameter. They are an important member of the one-dimensional carbon material family, compensating for the limitations of carbon nanotubes in application due to their small size. Carbon-based microtubes combine high aspect ratio, interconnected hollow channels, and excellent mechanical and electrical properties, significantly improving ion transport efficiency and structural stability, making them ideal carriers for next-generation electrodes, catalysts, and sensing materials.

[0003] Currently, the commonly used methods for preparing carbon microtubes mainly include: hard template method, chemical vapor deposition method, and hydrothermal method. The hard template method involves pre-synthesizing or selecting a hard template with a fixed morphology and size. A carbon precursor is coated onto the template surface through impregnation, coating, deposition, and polymerization. High-temperature carbonization transforms the carbon precursor into a rigid carbon layer. Finally, the hard template is removed using strong acids, strong bases, or hydrofluoric acid, resulting in hollow carbon tubes. However, this method involves many steps, is time-consuming, and requires numerous control steps, hindering efficient preparation. The chemical vapor deposition method involves the in-situ pyrolysis and deposition of gaseous carbon sources under high temperature and catalysis to form carbon-based microtubes. However, this method requires high temperature, continuous gas flow, and strict temperature control, resulting in high equipment and operating costs, which is not conducive to green and low-carbon synthesis. The hydrothermal method mainly uses anhydrous ethanol, ethylene glycol, toluene, hexabromobenzene, etc., as carbon sources, adding appropriate catalysts, and preparing the microtubes under high temperature and high pressure. However, hydrothermal products are mostly amorphous or low-graphitized carbon, making it difficult to produce high aspect ratio, continuous long carbon nanotubes.

[0004] The carbon microtubes prepared by the above methods require elemental doping through methods such as impregnation or high-temperature evaporation for further application in catalysis, ion batteries, and other fields. These doping processes are complex and suffer from drawbacks such as uneven dopant distribution, easy agglomeration, and weak bonding with the carbon microtube matrix. In summary, the current preparation and elemental doping modification conditions for carbon microtubes are quite demanding, necessitating a mild, simple, and easily scalable method for large-scale preparation and doping. Summary of the Invention

[0005] To address the shortcomings of existing carbon microtube fabrication techniques, such as numerous steps, long processing times, high costs associated with advanced processes, difficulty in pore size control, high raw material costs, potential toxicity, and limited large-scale production, this invention proposes a method for synthesizing multi-element-doped, diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template. The template, composed of a supramolecular structure of melamine, cyanuric acid, and its derivatives, offers advantages such as decomposability, adjustable diameter, and partial conversion into carbon-based materials. Furthermore, non-metallic elements such as phosphorus, sulfur, and oxygen can be added in one step to achieve doping. This method is simple, low-cost, and easily scalable for large-scale production.

[0006] To achieve the above objectives, this invention provides a method for synthesizing multi-element-doped, diameter-tunable carbon-based microtubes using supramolecular self-decomposing templates, comprising the following steps: (1) Melamine or 2,4,6-triaminopyrimidine and cyanuric acid or thiocyanic acid are dissolved in deionized water and heated and stirred. Then, the melamine or 2,4,6-triaminopyrimidine solution is added dropwise to the cyanuric acid or thiocyanic acid solution to obtain a supramolecular precursor.

[0007] (2) Add 2-methylimidazole and the element compound to be doped to the precursor solution in step (1) and heat and stir until the water evaporates. Place it in a forced-air drying oven to obtain the supramolecular precursor complex.

[0008] (3) After the precursor complex is calcined under an inert gas and cooled to room temperature, a multi-element doped carbon-based microtube is obtained.

[0009] Preferably, in step (1), the molar ratio of melamine or 2,4,6-triaminopyrimidine to cyanuric acid or thiocyanic acid is 1:1.

[0010] Preferably, the amount of 2-methylimidazole used in step (2) is 33%-50% of the molar amount of melamine.

[0011] Preferably, the heating and stirring temperature in step (2) is 90°C.

[0012] Preferably, the elemental compound in step (2) includes thiourea, sodium borohydride, sodium hypophosphite, or ammonium fluoride.

[0013] Preferably, the temperature of the drying oven in step (2) is 60°C and the drying time is 24 hours.

[0014] Preferably, the inert gas in step (3) is argon.

[0015] Preferably, in step (3), the temperature is increased to 500℃-700℃ at a heating rate of 5℃ / min and held for 1h-2h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention features a simple process, low raw material cost, concise operation, and convenient large-scale preparation. It uses a supramolecular structure composed of melamine, cyanuric acid, and their derivatives as a template, which has the advantages of being self-decomposable, having an adjustable diameter, and being composed of small carbon and nitrogen organic molecules, which can be partially converted into carbon-based materials during self-decomposition. At the same time, phosphorus, sulfur, oxygen, and other elements are added during the preparation of the precursor to achieve multi-nonmetallic element doping in one step. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing a carbon-based microtube according to a preferred embodiment of the present invention; Figure 2 The images show the carbon-based microtube precursor constructed according to the preferred embodiment 1 of the present invention and the SEM images of the prepared carbon microtube; (a) is a scanning electron microscope image of the carbon-based microtube precursor with a magnification of 1µm, and (b) is a scanning electron microscope image of the carbon-based microtube. Figure 3 This is an XRD pattern of the carbon-based microtube precursor constructed according to preferred embodiment 1 of the present invention; Figure 4 The images show the carbon-based microtube precursor constructed according to the preferred embodiment 2 of the present invention and the SEM images of the prepared carbon microtube; (a) is a scanning electron microscope image of the carbon-based microtube precursor with a magnification of 30µm, and (b) is a scanning electron microscope image of the carbon-based microtube with a magnification of 1µm. Figure 5 The images show the carbon-based microtube precursor constructed according to the preferred embodiment 3 of the present invention and the SEM images of the prepared carbon microtube; (a) is a scanning electron microscope image of the carbon-based microtube precursor with a magnification of 10µm, and (b) is a scanning electron microscope image of the carbon-based microtube with a magnification of 10µm. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise specified, all raw materials and reagents used in the embodiments are commercially available.

[0019] Example 1 (1) Dissolve 1g of melamine and 1.023g of cyanuric acid in 50ml of deionized water respectively. Heat and stir both for 15min. Then add the melamine solution dropwise to the cyanuric acid solution to obtain the supramolecular precursor.

[0020] (2) Add 0.3g of 2-methylimidazole to the supramolecular precursor solution, heat and stir at 90°C until the water evaporates, and then dry in a 60°C oven for 24 hours to obtain the supramolecular precursor complex.

[0021] (3) Place the precursor complex in a 10ml boat, wrap it with tin foil, make a number of small holes, heat it to 630℃ at 5℃ / min in a tube furnace under argon atmosphere, and keep it for 1h; after cooling, carbon-based microtubes are obtained.

[0022] Example 2 (1) Dissolve 1g of melamine and 1.41g of thiocyanate in 50ml of deionized water respectively. Heat and stir both for 15min. Then add the melamine solution dropwise to the thiocyanate solution to obtain the supramolecular precursor.

[0023] (2) Add 0.3g of 2-methylimidazole to the supramolecular precursor solution, heat and stir at 90°C until the water evaporates, and then dry in a 60°C oven for 24 hours to obtain the supramolecular precursor complex.

[0024] (3) Place the precursor complex in a 10ml boat, wrap it with tin foil, make a number of small holes, heat it to 500℃ at 5℃ / min in a tube furnace under argon atmosphere, and keep it for 2h; after cooling, carbon-based microtubes are obtained.

[0025] Example 3 (1) Dissolve 1g of 2,4,6-triaminopyrimidine and 1.42g of trithiocyanate in 50ml of deionized water respectively. Heat and stir both for 15min. Then add the 2,4,6-triaminopyrimidine solution dropwise to the trithiocyanate solution to obtain the supramolecular precursor.

[0026] (2) Add 0.3g of 2-methylimidazole to the supramolecular precursor solution, heat and stir at 90°C until the water evaporates, and then dry in a 60°C oven for 24 hours to obtain the supramolecular precursor complex.

[0027] (3) Place the precursor complex in a 10ml boat, wrap it with tin foil, make a number of small holes, heat it to 550℃ at 5℃ / min in a tube furnace under argon atmosphere, and keep it for 2h; after cooling, carbon-based microtubes are obtained.

[0028] Example 4 (1) Dissolve 1g of melamine and 1.023g of cyanuric acid in 50ml of deionized water respectively. Heat and stir both for 15min. Then add the melamine solution dropwise to the cyanuric acid solution to obtain the supramolecular precursor.

[0029] (2) Add 0.3g of 2-methylimidazole and 46mg of thiourea to the supramolecular precursor solution, heat and stir at 90°C until the water evaporates, and dry in a 60°C oven for 24h to obtain the supramolecular precursor complex.

[0030] (3) Place the precursor complex in a 10ml boat, wrap it with tin foil, make a number of small holes, heat it to 600℃ at 5℃ / min in a tube furnace under argon atmosphere, and keep it for 2h; after cooling, carbon-based microtubes are obtained.

[0031] Example 5 The difference between this embodiment and Embodiment 4 is that the doped element compound used in preparing the carbon microtube precursor composite is 23 mg of sodium borohydride.

[0032] Example 6 The difference between this embodiment and Embodiment 4 is that the doped element compound used in preparing the carbon microtube precursor composite is 50 mg of sodium hypophosphite.

[0033] Example 7 The difference between this embodiment and Embodiment 4 is that the doped element compound used in preparing the carbon microtube precursor composite is 23 mg of ammonium fluoride.

[0034] In specific embodiments 1-3, any one of the elemental compounds, such as thiourea, sodium borohydride, sodium hypophosphite, or ammonium fluoride, can be used for doping.

[0035] Characterization Tests and Results Description The undoped carbon microtubes and their precursors obtained in Examples 1-3 were characterized by SEM, and the results are as follows: Figure 2 , Figure 4 , Figure 5 As shown in the figure, the carbon-based microtubes prepared from three different raw materials—melamine-cyanuric acid, melamine-thiocyanic acid, and 2,4,6-triaminopyrimidine-thiocyanic acid—have different diameters, ranging from 0.2 to 1 µm. All exhibit regular microtube morphologies and uniform diameter distribution. This indicates that this experiment synthesized micron-sized hollow tubular structures with adjustable diameters via a supramolecular self-templating method.

[0036] The undoped carbon microtube precursor obtained in Experiment 1 was characterized by XRD, and the results are as follows: Figure 3 As shown, the target product is composed of carbon nitride. XRD clearly shows that the prepared microtube precursor is a carbon nitride material, and no metal-related diffraction peaks were found, indicating high phase purity. This confirms that the synthesized precursor is a pure-phase carbon nitride-based microtube.

[0037] In this invention, Examples 4-7 illustrate the preparation method of element-doped carbon microtubes. By introducing elemental compounds during the preparation of the precursor, the preparation of multi-element-doped carbon-based microtubes can be achieved in one step. This doping method does not destroy the original tubular morphology of the carbon microtubes, but can only control the surface defects, conductivity and electrochemical performance of the material.

[0038] In Experimental Examples 1-7 of this invention, the nitrogen-rich compound 2-methylimidazole is introduced during the synthesis of the precursor. This can play a supramolecular structure guiding role in the assembly of the precursor, which is beneficial for controlling the morphology of the product. At the same time, it serves as an abundant nitrogen source, which improves the nitrogen doping of the product.

[0039] This invention provides a method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using supramolecular self-decomposing templates. Different combinations of melamine and cyanuric acid and their derivatives are used to synthesize carbon-based microtubes with tunable diameters. The method has low raw material costs, can achieve doping of multiple non-metallic elements in one step during the synthesis of precursors, is simple to operate, has low process costs, and is convenient for large-scale preparation.

Claims

1. A method for synthesizing multi-element-doped, diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template, characterized in that, Includes the following steps: (1) Mix the dissolved melamine or 2,4,6-triaminopyrimidine solution with cyanuric acid or trithiocyanic acid solution, heat and stir to form supramolecular precursors of different diameters; (2) Add 2-methylimidazole and doped element compound to the product in step (1) to achieve multi-element doping in one step, continue heating and stirring until the water evaporates, and put it into a forced-air drying oven to dry to obtain supramolecular precursor complex. (3) The precursor complex is obtained by calcining under an inert gas.

2. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, The different raw material combinations include melamine and cyanuric acid, melamine and thiocyanate, and 2,4,6-triaminopyrimidine and thiocyanate. The three systems yield carbon-based microtubes with diameters ranging from 0.2 to 1 µm.

3. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, The elemental compound in step (2) is thiourea, sodium borohydride, sodium hypophosphite, or ammonium fluoride.

4. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, In step (1), the solvent is deionized water.

5. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, In step (1), the molar ratio of melamine or 2,4,6-triaminopyrimidine to cyanuric acid or thiocyanic acid is (1:1), and in step (2), the molar ratio of 2-methylimidazole to cyanuric acid or thiocyanic acid is (1:2)-(1:3).

6. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, In step (1), melamine or 2,4,6-triaminopyrimidine solution is added dropwise to cyanuric acid or thiocyanic acid solution.

7. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, The inert gas mentioned in step (3) is argon, the heating rate is 5℃ / min, the temperature is raised to 500℃-700℃, and held for 1h-2h.

8. The method for synthesizing multi-element doped diameter-tunable carbon-based microtubes using a supramolecular self-decomposing template according to claim 1, characterized in that, In step (2), the temperature of the drying oven is 60℃ and the drying time is 24h.

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